The present invention relates to a surgical fastener or device (implant) formed in the shape of an arrow comprising a shaft with a proximal (first) portion having a blunt end and tapered form, such that the proximal portion is broad at its blunt end and tapers in the direction of a distal (second) portion of the shaft, the distal portion having protrusions and a pointed end, wherein the tapered form of the proximal portion and the protrusions of the distal portion are configured to lock the implant in a position inside a soft and/or tough tissue according to the use of the implant. The implant may be manufactured of a polymer or a polymeric compound which is substantially (bio)absorbable (resorbable) after implantation in tissue and contains an oriented reinforcing structure or the like of a polymer or polymeric compound or ceramic bioactive glass compound.
The surgical implant of the invention is particularly, but not solely, suitable for use in surgically repairing traumas of soft and/or tough tissues containing fibrous structures, such as knee meniscal tissues.
With reference to the prior art in the field, it has been shown that fixation of meniscus traumas, like ruptures and lesions, by suturing with absorbable sutures gives better results than removal of traumatized meniscal tissue, see e.g. N. A Palmeri, T. F. Winters, A. E. Joiner and T. Evans, xe2x80x9cThe Development and Testing of the Arthroscopic Meniscal Staplexe2x80x9d, Arthroscopy, Vol. 5, No. 2, 1989, p. 156, the entire disclosure of which is incorporated herein by reference. However, arthroscopic suturing is a complicated and tedious technique where risks for the patient are significant because of danger to vessels and nerves. Additionally, the suturing of meniscus ruptures leaves a single or several loops of sutures on the meniscal surface, which can irritate joint cavity tissues. Therefore, for a long time surgeons have desired an absorbable meniscus lesion fixation device, like a staple or fastener, which has the advantages of absorbable suturing techniques but which can be used more rapidly and safely than sutures.
Several research groups have tried to develop absorbable meniscus lesion fixation devices, such as clamps. However, the various demands upon such a device are high. It must be strong enough to maintain good contact with the lesion tissues after the operation so that rapid healing occurs, while retaining its strength long enough to ensure good healing. It also must be absorbed without causing complications that would prevent the healing of the lesion. Additionally, the installation of the device should be easy and rapid and should cause minimum operational trauma. Because of these high demands, an optimal absorbable meniscus lesion fixation device has not been developed yet. Palmeri et al., supra, reported the development of a method of meniscal repair using arthroscopically applied absorbable fasteners. However, the reported method was complicated because the final design used cannulation of the staple for needle-guided placement. Additionally, staple fracture, migration and articular abrasion was found.
With regard to implants known in this field, reference is made to U.S. Pat. No. 4,873,976, the entire disclosure of which is incorporated herein by reference, which patent discloses an arrow-like implant particularly intended for the surgical repair of meniscal ruptures. However, the arrow-like implant according to that patent has the disadvantage that its proximal end (stem) is shaped as a plate in a way that the direction of the main plane of the plate is perpendicular to the longitudinal direction of the arrow""s body. Because of this fact, it is particularly difficult to install the implant, because the channel used to install the implant must have the cross-sectional shape of the stem; thus, it is difficult to guide the implant in the installation channel, because the guiding effect is substantially brought upon the stem only, but not the body of the arrow due to its shape. Furthermore, the structure of the stem causes tissue irritation and abrasion, particularly when placed in connection with the meniscus because the stem is usually left protruding to a high degree from the outer surface of the meniscus.
Bays et al. (U.S. Pat. Nos. 4,884,572 and 4,895,141, the entire disclosures of which are incorporated herein by way of this reference) describe a surgical-repair tack and applicator and method of using them. The tack has a barb member, a shaft portion and a grip portion. The tack is made of biodegradable material having a degradation time selected to coincide with the healing time of the tissue. In an alternative embodiment, the tack""s barb comprises a continuous helical barb. A disadvantage of this tack is that the grip portion is bulky and may remain on the meniscal surface, causing irritation inside a joint cavity.
The method and apparatus for repairing a meniscal tear disclosed by Winters (U.S. Pat. No. 5,059,206, the entire disclosure of which is incorporated herein by way of this reference) comprises a fastener having protrusions or barbs that is applied to a meniscal tear with a delivery device. The delivery device has a flexible tip that is manipulable through a curved radius to enable the surgeon to insert the device into the central part of the knee and then extend the fastener radially outward into and across a meniscal tear. Also in this case, the proximal end of the fastener is bulky comprising a cylindrical end (head member) which protrudes partially above and/or below the outer surface of the meniscus.
Tamminmxc3xa4ki et al. (U.S. Pat. No. 5,562,704, the entire disclosure of which is incorporated herein by way of this reference) disclose an arrow-like bioabsorbable implant particularly intended for the surgical repair of meniscal ruptures. This implant does not have the guiding or abrasion problems that the implants of U.S. Pat. No 4,873,976 or U.S. Pat. No. 5,059,206 may have. However, a disadvantage of the device of U.S. Pat. No. 5,562,704 is that the proximal part of the implant (the wings) preferably remains on the surface of the meniscus, so that when the wings break as a consequence of bioabsorption, the broken wings may irritate knee joint tissues. Moreover, if the proximal part with the wings is desired to be located inside of meniscal tissue, the surface capsule of the meniscus must be cut horizontally with a special cutting blade. This lengthens the operation time and causes substantial damage to the meniscus surface.
U.S. Pat. No. 5,569,252, the entire disclosure of which is incorporated herein by way of this reference, describes a fastener, an installation device, and method for repairing tears in the soft tissue of a patient, including meniscal tears. The fastener has a variable-pitch helical protrusion along a central portion that decreases from the distal end to the proximal end, which can serve to bring two sides of the tear into opposition as the fastener is advanced across the two sides of the tear in a screwing motion. This implant, which needs a screwing motion for installation, is slow and tedious to use arthroscopically and the turning of the implant through fibrous tissue, such as meniscus tissue, has the risk that the fibrous tissue may twist around the turning implant, hindering or preventing the installation of the implant.
Orthopedic and Musculoskeletal Markets Biotechnology and Tissue Engineering, Medical Data International, Inc., Irvine, Calif. USA, February 1997, p. 1-17, the entire disclosure of which is incorporated herein by way of this reference, describes a bioabsorbable device for meniscal repair. This device has two legs with molded barbs that are attached by a flexible member composed of resorbable suture. The device is installed into a meniscus with an arthroscopic tool, so that the legs penetrate the rupture of the meniscus to hold the edges together. The disadvantage of this device is that the suture loop remains on the surface of meniscus where it can cause irritation. Additionally, this two-leg device requires a bulky installation tool which makes arthroscopic installation of the device difficult.
U.S. patent application Ser. No. 08/887,130, the entire disclosure of which is incorporated herein by way of this reference, describes a fastener for body tissue repair comprising: a shaft comprised of a proximal portion, having an upper surface and a lower surface with first protrusions, and a distal portion, said distal portion having a sharpened tip and one or more first protrusions, wherein said first protrusions have proximal surfaces configured to arrest the movement of the shaft in the proximal direction and distal surfaces configured to permit the movement of the shaft in the distal direction, said proximal portion having second protrusions on the upper surface and lower surface of the proximal portion, wherein said second protrusions have distal surfaces configured to arrest the movement of the shaft in the distal direction. Although this implant sinks totally inside a tissue,-like a knee meniscus, the second protrusions can be damaged, e.g., bent or broken, during the insertion of the implant into tissue, or the second protrusions can damage the tissue, e.g., by cutting the horizontal collagen fibers of the tissue during the insertion.
Therefore, it is an object of the present invention to provide a bioabsorbable fastener that allows a minimally invasive method for repairing a tear in soft or tough tissue.
It is a further object of the invention to provide such a fastener that is rapid and easy to install and gives a strong and safe fixation of the tissue tear and that may be made from a nontoxic, biocompatible bioabsorbable polymer, polymer alloy or fiber reinforced polymer composite, specially designed to maintain its structural integrity during the healing of the tear and to prevent tissue abrasion. It is an additional object to provide such a fastener having a shape designed to compress the tear.
It is a further object of the invention to provide a device (fastener) which will be shot or pushed totally inside of soft or tough tissue, like meniscal tissue, to penetrate the tissue (meniscal) tear and to hold the ruptured edges together and to cause a minimal trauma to the tissue through which the fastener forces its way. These and other objects are attained with the fastener of the present invention.
The fastener of the present invention is designed for repairing a tear in soft and/or tough tissue of a patient, such as a tear of the meniscus within the knee. The surgical fastener or device (implant) of the present invention has been formed in the shape of an arrow comprising a shaft with a proximal (first) portion having a blunt end and tapered form so that the blunt end of the proximal portion is broad and it tapers in the direction of a distal (second) portion of the shaft, the distal portion having protrusions and a pointed end, the tapered form of the proximal portion and the protrusions of the distal portion configured to lock the implant in a position inside a soft and/or tough tissue according to use of the implant. Accordingly, protrusions emerge from the distal portion of the device. The protrusions are typically barbs, scales, threads, serrations, ridges or the like. These protrusions at the distal portion of the shaft of the device prevent the installed device from slipping out of the meniscal tissue in the direction opposite to the direction of installation. At least one or more of the protrusions must penetrate the rupture plane inside of the tissue, to lock the distal portion of the device into the tissue at a position distal of the tear. The tapered form of the proximal portion of the shaft allows the penetration of the shaft into the meniscal tissue when the fastener is pushed, shot or hammered into the tissue. Because of the tapered structure, the penetration of the proximal portion of the shaft into the meniscal tissue causes minimal damage, because the penetrating, tapered proximal portion does not cut the horizontal collagen fibers of meniscal tissue, but separates them from each other when the proximal portion forms a cavity for itself in the meniscal tissue. The opening of such a cavity inside of meniscal tissue for the tapered proximal portion requires a substantial amount of external pushing force from the installation device, which pushes the fastener into the meniscal tissue. When the fastener is totally inside of the meniscus and the pushing force is ended, the fastener stops inside of the meniscal tissue and the tapered proximal portion prevents the further penetration of the fastener into the meniscal tissue. In this way, the combined effect of the distal protrusions and the proximal tapered portion lock the fastener effectively inside of the meniscus, to close and fix the meniscal rupture to enhance its healing.
In a preferred embodiment of the present invention, the protrusions of the distal portion of the shaft of the device are formed so that they facilitate the slipping of the device into the meniscus during insertion, while resisting the slipping of the device in the direction opposite to the installation direction. On the other hand, the tapered proximal portion of the shaft of the device is formed so that it stops the device inside of the meniscal tissue when the device has been pushed or shot into the meniscus with the delivery (installation) tool. Both distal protrusions and the proximal tapered portion of the device of the invention, acting together, exert an advantageous compression on the ruptured surface when the device of the invention is shot into the meniscus and across the rupture. This compression serves to close the rupture and promotes healing.
A further advantageous feature of the device is that the surface of the shaft may include longitudinal ridges. The ridges promote healing of the rupture by providing channels along the interiors of the ridges through which beneficial blood flow can occur along the length of the device. These channels, which are typically about 0.05-0.5 mm wide, act as capillaries, transporting blood from the highly vascularized distal portion (outer periphery) of the meniscus to the poorly vascularized proximal portion (inner periphery) of the meniscus. Further, the ridges help to guide the fastener through the cannula of the installation instrument and into the meniscal or other soft tissue during installation.